Acne keloidalis nuchae (AKN) is a condition characterized by follicular-based papules and pustules that form hypertrophic or keloid-like scars. AKN typically occurs on the occipital scalp and posterior neck and develops almost exclusively in young, African-American men.  The term acne keloidalis nuchae is somewhat of a misnomer because the lesions do not occur as a result of acne vulgaris, but rather a folliculitis. Moreover, histologically lesions are not keloidal. 
Acne keloidalis nuchae was first recognized as a discrete entity in the late 1800s. Hebra was the first to describe and document this condition in 1860, under the name sycosis framboesiformis. Subsequently in 1869, Kaposi described this same condition as dermatitis papillaris capillitii.  The term acne keloidalis was then given to this condition in 1872 by Bazin, and, since that time, this is the name most often used in the literature. 
Lesions initially manifest as mildly pruritic follicular-based papules and pustules on the nape of the neck. Chronic folliculitis ultimately leads to development of keloid-like plaques. AKN develops in hair bearing skin areas, and broken hair shafts, tufted hairs, and ingrown hairs can be identified within and at the margins of the plaques themselves. Lesions can grow over time and become disfiguring and painful. In advanced cases, abscesses and sinus tracts with purulent discharge may develop. Unlike true acne vulgaris, comedones are not a common feature of AKN.
The exact etiology of AKN is unclear. It is thought that chronic irritation from coarse, curly hairs in the skin leads to inflammation and development of these lesions. This hypothesis is supported by the fact that close shaving and chronic rubbing of the area by clothing or athletic gear make AKN worse. In a study of 453 high school, college, and professional American football players, 13.6% of African American athletes had acne keloidalis nuchae, as opposed to none of the Caucasian athletes.  It has also been shown that men who have haircuts more frequently than once a month are at higher risk of developing acne keloidalis nuchae. 
Pseudofolliculitis barbae (PFB) is a similar condition that occurs commonly in African Americans. In PFB, it has been proposed that close shaving of coarse, curved hairs facilitates the reentry of the free end of the hair into the skin (via either extrafollicular or transfollicular penetration), which then invokes a chronic foreign-body inflammatory response.
While ingrowing hairs may account for small papules, they do not sufficiently explain the progressive scarring alopecia that occurs in some patients. These patients with scarring alopecia often exhibit recurrent crops of small pustules and may have a condition akin to folliculitis decalvans. Chronic low-grade bacterial infection, autoimmunity, and some types of medication (eg, cyclosporine, diphenylhydantoin, carbamazepine) have also been implicated in the pathogenesis in some patients. [6, 7]
Sperling et al classify acne keloidalis nuchae as a primary form of inflammatory scarring alopecia and suggest that overgrowth of microorganisms does not play an essential role in the pathogenesis of AKN. They also found no association between pseudofolliculitis barbae and acne keloidalis nuchae. 
After extensive histological and ultrastructural studies of AKN lesions, Herzberg et al proposed that a series of events must happen in order for acne keloidalis nuchae to occur, namely the following  :
The initial process begins as acute perifollicular inflammation followed by weakening of the follicular wall at the level of the lower infundibulum, the isthmus, or both.
The naked hair shaft is then released into the surrounding dermis, which acts as a foreign-body and incites further acute and chronic granulomatous inflammation. This process is clinically manifested by small follicular-based papules and pustules. The nape of the neck has almost twice the number of mast cells compared with the anterior scalp and therefore may contribute to the pruritic sensation in this location. 
Subsequently, fibroblasts deposit new collagen and fibrosis ensues.
Distortion and occlusion of the follicular lumen by the fibrosis results in retention of the hair shaft in the inferior aspect of the follicle, thereby perpetuating the granulomatous inflammation and scarring. This stage is marked by plaques of hypertrophic scar and irreversible alopecia.
Acne keloidalis nuchae is said to represent 0.45% of all dermatoses affecting black persons. 
Acne keloidalis nuchae is most prevalent in African Americans; however, it has occasionally been reported in Hispanics and Asians, and, rarely, in whites.
Most cases occur in persons aged 14-25 years. Lesions manifesting prior to puberty or in persons older than 50 years is unusual. 
The prognosis is good if acne keloidalis nuchae is treated early and properly. However, once major scarring develops, therapy is more difficult and morbidity is increased. The plaques of acne keloidalis nuchae slowly expand over time, and, although medically benign, acne keloidalis nuchae can be a psychologically devastating condition. Chronic pruritus and drainage may occur, and, ultimately, scarring alopecia may ensue.
Educate patients on the postulated underlying causes of acne keloidalis nuchae. Advise patients to discontinue wearing possible offending garments.Instruct patients to tell their barbers not to shave the posterior part of their hairline. Counsel patients about scalp folliculitis and how to care for it.
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